This proposal is a continuation of our investigation of rattlesnake (genera Sistrurus and Crotalus) genealogy utilizing data from morphology, SEM scale surface analysis, G and C banded karyotypes, DNA hybridization, and most intensely, gel electrophoresis of allozymes. Drawing upon a previously resolved evolutionary tree, we will analyze possible hybridization between sister species of rattlesnakes (using the above techniques) and reassess their taxonomic status. Our efforts will then address those pit vipers most closely related to the rattlesnakes, the moccasins (genera Aokistrodon, Hypernale, Dienagkistrodon, and Calloselasma). The same techniques will be employed to establish the phylogenetic position of these genera and their species, first relative to other pit vipers, and then relatives to each other, thereby generating the first cladistic evolutionary tree ever generated for these organisms. The resulting tree should provide a valuable resource for toxicologists searching for natural groups of species - in order to develop sets of monoclonal antibodies, or tot draw up as pharmacological resources for medically valuable enzymes. All student trainees will be rotated through each of the five major protocols. Library Search training will precede and computer analysis will follow these rotations. Each student will be assigned particular short term investigations leading to prompt publication. As a result they should develop competence (and self-confidence) in a wide rage of biomedically valuable skills. A cost efficient group presentation of prior student work is planned for the First World Herpetology Congress in London, and a second trip to China, hosted by our sister University in Wuhan, will give MBRS students access to 55% of all our required snake species on a single excursion.